Gas-cooled turbine blade

ABSTRACT

A cooled turbine blade for gas turbines and the like having passageways for conducting a relatively cool fluid through the blade to its tip and incorporating a walled cavity at the tip of the blade. The wall of the cavity has a cutaway portion which permits the cooling fluid to discharge into a main gas stream through the turbine at the area of lowest pressure on the blade surfaces. This permits the flow of fluid from the discharge orifices of the passageways to be more uniform from the leading to the trailing edge of the blade and reduces the required gas pressure on the entire cooling system.

United Mates Patent Metaier, ,11", 1 Jan, 11%, W72

[54] GAfi-(IUOLED TURBINE BLADE 3,533,712 10/1970 Kercher ..41-6/97 X[72] Inventor: Charles Walter Metzler, .llr., Springfield, FOREIGNPATENTS 0 ppuc o s 920,641 1 1/1954 Germany ..4l6/97 [73] Assignee:Westinghouse Electric Corporation, Pittsburgh, Pa. PrimaryExaminer-Everette A. Powell, Jr. Filed. Dec 23 1969 Attorney-A. T.Stratton, F. P. Lyle and IF. Cristiano, Jr.

[21] Appl. No.: $87,544 [57] ABSTRACT A cooled turbine blade for gasturbines and the like having 52 11.s.c1 ..4116/96, 416/92, 416/97passageways for conducting a relatively c001 fluid through the 51 1m.(:1 ..]F01d s/w blade to its tip and incorporating a Walled cavity atthe p of 53 Field ofSearch ..4l6/96, 97, 92, 95 the blade The Wall Ofthecavity has a cutaway P" which permits the cooling fluid to dischargeinto a main gas stream 6 R E d through the turbine at the area of lowestpressure on the blade [5 l e erences l e surfaces. This permits the flowof fluid from the discharge ori- UNITED STATES A EN S fices of thepassageways to be more uniform from the leading to the trailing edge ofthe blade and reduces the required gas 2,888,243 5/1959 Pollock 416/92pressure on the entire cooling System 3,057,597 10/1962 Meyer eta.....416/92 3,164,367 1/1965 Lynch .416/96 X 41 Cinims, 4 DrawingFigures GAS-COOLED TURBINE BLADE I BACKGROUND OF THE INVENTION Inconstructing turbine blades for gas turbine engines, numerousdifficulties are encountered in their design because of the high speedsat which such blades operate and because of the high temperatures towhich they are subjected. The temperature of a blade may be heldmaterially lower than that of the gases in which it operates byproviding cooling passages in the blade extending from its root to itstip and by conducting a stream of cooling fluid, such as air, throughthese passageways to cool the blade.

Normally, the cooling passages terminate at openings in the extreme endor tip of the blade. This, however, has several disadvantages. First,the pressure on the blade at its leading edge is greater than at itstrailing edge. As a result, the cooling fluid in the passages at theleading edge must discharge into an area of greater pressure than thepassages at the trailing edge, meaning that the flow of fluid and heattransfer efficiency at the leading edge is impeded. Secondly, the tipclearance between the end of the blade and the stationary turbine wallmust be greater than it otherwise would be; and the tolerances becomemore critical. Finally, the pressure on the cooling fluid must beincreased to the point where it can be effectively discharged into ahigh-pressure gas stream.

SUMMARY OF THE INVENTION In accordance with the present invention, theforegoing drawbacks associated with prior art cooling systems areovercome by a construction wherein the blade is provided with a walledcavity at its tip. The cooling passages terminate at the bottom of thecavity; while the extremity of the cavity wall is adjacent the turbinecasing, and, in effect, constitutes the end of the blade. A portion ofthe wall is cutaway on the low-pressure side of the blade adjacent itstrailing edge such that the passages in the blade do not discharge intothe main turbine gas stream but rather into a relatively constantpressure area within the cavity. Furthermore, by virtue of the fact thatthe wall of the cavity is cut away adjacent to the trailing edge of theblade on its low-pressure side, the cavity is exposed to the lowestdischarge pressure possible with a minimum disturbance to the main flowthrough the turbine. Thus, the pressure on the cooling system can bereduced and, at the same time, the flow offluid through the coolingpassages from the leading edge of the blade to its trailing edge isessentially the same throughout.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specification.I

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I is a fragmentaryelevational view of a turbine rotor having the blades of the inventionthereon;

FIG. 2 is a top view taken substantially along line II-II of FIG. I, buton a larger scale, showing the walled cavity tip construction of theblades of the invention;

FIG. 3 is a cross-sectional development view through the curved centerof a blade taken substantially along line III-III of FIG. 2; and

FIG. 4 is a perspective view of the blade tip ofthe invention.

With reference now to the drawings, and particularly to FIG. 1, there isshown, by way of example, part of a gas turbine rotor structureincluding a rotor shaft which is connected to a rotor disc 12 projectingradially from the shaft axis. The rim 14 of the disc 12 is formed with acontinuous se ries of transverse side entry" recesses 16, each of whichis broadly V-shaped but having sidewalls formed with adjacent secondarytransverse serrations or grooves 17.

The turbine blades 18, as perhaps best shown in FIGS. 2 and 4, have theusual airfoil shape with rounded leading edges 20, thin trailing edges22 and curved profiles. The blade root 24 (FIG. I is in the form of atriangular elongated block with the blade Id integral with its one sideand the two other sides having adjacent transverse grooves therein,which grooves conform to and are adapted to register with the grooves I7formed in the transverse recesses I6 of the disc rim M, thus forming thewell-known fir tree base connection. Attachment is made by sliding theblade root into the disc rim recess so that the grooves and ridges ofthe two parts are in cooperative engagement. Suitable means, not shown,are provided for maintaining the roots 24 within their cooperatingrecesses 16. Furthermore, suitable means, not shown, but well within theskill of the art, are provided for conducting a cool ing fluid such asair up through the root portions 241 and into radial passages extendingthrough each of the blades I8.

The radial passageways 26 are shown in FIGS. 2, 3 and 4 and extend allthe way from the root 24 to the tip or outer radial extremity of eachblade. The lower sides of the blades I8 as viewed in FIG. 2 are referredto as the high-pressure sides 29 and are those sides against which hotgases under pressure are directed in order to cause the rotor to turn inthe direction of arrow 30 shown in FIG. I. The other side 32 of eachblade also extends between the leading and trailing edges 20 and 22 andis referred to as the low-pressure side. Hot gases, in passing throughthe blades, generally follow the path of arrows 34. The point of highestpressure on the blades is at the high-pressure side 29 adjacent theleading edge 20. As the gas travels from the leading to the trailingedge of the blade, it expands and its pressure reduces. Consequently,the point of lowest pressure is at the low-pressure side 32 near thethroat area B.

In accordance with the present invention, the tip of each blade I8 isprovided with a walled cavity, generally indicated by the referencenumeral 36 in FIGS. 24, which is formed by a wall 38 extending along thetop of the high-pressure side 29 from the trailing edge 22 to theleading edge 20 and thence along approximately one-half the length ofthe low-pressure side 32 to point A which is just downstream of thethroat B between the trailing edge 22 of one blade and the low-pressureside of the following blade. The radial passageways 26 terminate at thebottom 37 of the cavity 36, as perhaps best shown in FIG. 3. In thismanner, the gas discharges into an area within the cavity 36 ofrelatively constant pressure, meaning that the pressure which gasesissuing from the passageways 26 at the leading edge 20 experience isapproximately the same as that experienced by the gas leaving thepassageways 26 adjacent the trailing edge 22. The depth of the cavity 36is adjusted to provide an area at C which is substantially greater thanthe combined area of the cross sections of the cooling passages 26upstream of point A. This permits the discharge pressure for theupstream holes to approach the pressure at point A, approximately thelowest pressure on the blade surface.

The present invention thus provides a means for attaining a uniform flowof cooling fluid through radial passages in a turbine blade from itsleading to its trailing edge, independent of operating tip clearancesbetween the Iblade tip and the stationary turbine walls. At the sametime, the cooling air enters the main stream through the turbine in morenearly the correct direction for mixing with the main gas stream,thereby reducing mixing losses. Although the invention has been shown inconnection with a certain specific embodiment, it will be readilyapparent to those skilled in the art that various changes in form andarrangement of parts may be made to suit requirements without departingfrom the spirit and scope of the invention.

I claim as my invention:

1. In a turbine blade of the type having a root portion, a tip portion,leading and trailing edge portions, a low-pressure surface extendingbetween said leading and trailing edges. a highpressure surfacecontinuous with said low-pressure surface and extending between saidleading and trailing edges, and a plurality of passages of uniformcross-sectional area extending from said root portion to said tipportion of the blade for con ducting a cooling fluid through the blade;the improvement comprising a walled cavity at the outermost tip portionof said blade having a bottom at which said passages terminate and acutaway portion in its wall extending between said trailing edge and apoint on said low-pressure side which permits the cooling fluid todischarge into the main gas stream through the turbine at the point ofsubstantially lowest pressure on the blade surfaces, and said wall beinga continuous extension of the outer high-pressure and low-pressuresurfaces.

2. The improvement of claim 1 wherein said point is opposite thetrailing edge of a next successive turbine blade when said blades areassembled on a rotor.

1. In a turbine blade of the type having a root portion, a tip portion,leading and trailing edge portions, a low-pressure surface extendingbetween said leading and trailing edges, a high-pressure surfacecontinuous with said low-pressure surface and extending between saidleading and trailing edges, and a plurality of passages of uniformcross-sectional area extending from said root portion to said tipportion of the blade for conducting a cooling fluid through the blade;the improvement comprising a walled cavity at the outermost tip portionof said blade having a bottom at which said passages terminate and acutaway portion in its wall extending between said trailing edge and apoint on said low-pressure side which permits the cooling fluid todischarge into the main gas stream through the turbine at the point ofsubstantially lowest pressure on the blade surfaces, and said wall beinga continuous extension of the outer high-pressure and low-pressuresurfaces.
 2. The improvement of claim 1 wherein said point is oppositethe trailing edge of a next successive turbine blade when said bladesare assembled on a rotor.
 3. The improvement of claim 1 wherein the areabetween the point on said low-pressure side where said wall terminatesand the opposite wall on the high-pressure side of the blade issubstantially greater than the combined areas of the cross sections ofthe passages upstream of said point between said point and said leadingedge.
 4. The improvement of claim 1 wherein said blade is of airfoilconstruction with a rounded leading edge portion of greater radius thanthe trailing edge portion.